1. Technical Field
This invention relates generally to carrier tapes of the kind used to transport components from a component manufacturer to a different manufacturer that assembles the components into new products. More specifically, this invention relates to carrier tapes for storing electronic surface mount components and for supplying those components seriatim to a machine.
2. Description of the Related Art
In general, carrier tapes that are used to transport components from a component manufacturer to a different manufacturer that assembles the components into new products are well known. For example, in the field of electronic circuit assembly, electronic components are often carried from a supply of such components to a specific location on a circuit board for attachment thereto. The components may be of several different types, including surface mount components. Particular examples include memory chips, integrated circuit chips, resistors, connectors, dual in-line processors, capacitors, gate arrays, etc. Such components are typically affixed to a circuit board that may later be incorporated into an electronic device.
Rather than manually affixing each individual electronic component to a circuit board, the electronics industry makes extensive use of robotic placement machines, sometimes known as "pick-and-place" machines, which grasp a component at a specific location (the supply) and place it at another specific location (the circuit board). To ensure the sustained operation of the robotic placement machine, a continuous supply of electronic components must be furnished to the machine at a predetermined rate and location to permit the machine to be programmed to repeat a precise sequence of movements during every cycle. It is therefore important that each such component be located in the same position (i.e. the point at which the robotic placement machine grasps the component) as each preceding and succeeding component.
One way to provide a continuous supply of electronic components to a desired location is to use a carrier tape. Conventional carrier tapes generally comprise an elongated strip that has a series of identical pockets formed at predetermined, uniformly spaced intervals along the length of the tape. The pockets are designed to receive an electronic component. A continuous cover tape is applied over the elongated strip to retain the components in the pockets. The tapes also normally include a series of through holes uniformly spaced along one or both edges of the elongated strip. The through holes receive the teeth of a drive sprocket that advances the tape toward the robotic placement machine.
Each pocket is shaped to closely receive the electronic component. Frequently, the pockets are sized to match a particular component. In fact, the tolerances between the component and the pocket walls may be quite small such that a given carrier tape may only be useful with a single size of component. Thus, a component of a different size would require a new pocket design. In conventional carrier tapes, if the pockets are not properly sized for the stored component, the component may rotate within the pocket making subsequent removal by automatic pick-up equipment difficult or impossible since these devices require precise component orientation for proper removal. A component may even turn over within its pocket during shipping, necessitating reorientation of the stored component. Excessive component movement may also result in a component becoming damaged as it collides with the pocket walls. Given these variables, it can be expensive to design, manufacture and store a multitude of different carrier tapes having different pocket designs for different components.
Eventually, the carrier tape is fed to a robotic placement machine that strips the continuous cover tape from the carrier and removes the components from the pockets and places them onto the circuit board. Removal of the component is commonly accomplished with a vacuum pick-up device that grasps the top of the component by suction. The vacuum pick-up may be assisted by a push-up needle or probe that penetrates a hole formed in the floor of the pocket to push up against the component. The removed cover tape is waste that must be gathered and disposed.
U.S. Pat. No. 4,778,326 (Althouse et at.) discloses a carrier that is adapted for handling semiconductor chips and other smooth-surfaced articles. The carrier includes a base that has a recess within its interior. The recess includes a plurality of protuberances that support a thin flexible film cover that overlies the base. Semiconductor chips are carded on the upper surface of the cover. By connecting the base to a vacuum, the cover can be drawn down into the base recess and against the protrusions. This converts the cover from a flat condition in full surface contact with the semiconductor chip to a wavy or undulating condition having reduced surface contact with the semiconductor chip. Reportedly, the reduced surface area contact facilitates removal of the semiconductor chip.
However, Althouse et al. note that while their invention is adapted for use with a wide variety of chip sizes, the number and the size of the protuberances employed in the base are selected in relationship to the size of the chips to be handled. As a result, a chip which is too small for proper use with the carrier could be drawn down with the cover into a recess and its removal from the carrier would not be facilitated.
U.S. Pat. No. 4,667,944 (Althouse) discloses a related device in which a textured fabric is sandwiched between the cover and the base. To facilitate removing the semiconductor chip from the cover, surface contact between the cover and the chip is reduced by drawing portions of the cover into crevices in the upper face of the textured fabric by applying a vacuum thereto.
Although the invention is apparently adapted for use with a wide variety of chip sizes, Althouse notes that among the factors to be considered in selecting the textured fabric is the size of the devices to be handled.
U.S. Pat. No. 5,089,314 (Masujima et al.) discloses a carrier tape for surface mounted electronic circuit elements which includes a tape body having an adhesive applied thereto. The adhesive is formed of a material that does not exhibit any adhesion at a normal temperature but which does exhibit adhesion when heated to a temperature of about 80.degree. C. The adhesive may be a silicone, an acrylic resin, or a mixture of silicone and acrylic resin. When the electronic circuit element is removed from the carrier, the adhesive transfers to the bottom of the circuit element. The circuit element and the adhesive are then heated such that the adhesive can provisionally bond the circuit element to a printed circuit board.
U.S. Pat. No. 4,966,281 to Kawanishi et al. discloses an electronic component carrier having a series of electronic component-mounting portions that include a layer of adhesive. The adhesive is a rubber type, an acryl type or a silicone type having suitable pressure sensitive adhesive properties. The use of a push bar enables smooth removal of the electronic component from the adhesive layer.
However, there is still a need for a carrier tape that can securely retain a stored component in the proper orientation for subsequent removal by an automated device. It would be highly desirable if this could be accomplished without the need for separate carrier tapes for different component sizes and designs. It would also be highly desirable if this could be accomplished without using a cover tape. Such carrier tapes would offer even further advantages if any adhesive used to retain the components on the carrier tape did not display pressure sensitive adhesive properties because tacky pressure sensitive adhesives can retain dirt and other potential contaminants. Similarly, it would be useful if the adhesive did not transfer to the stored component upon removal of the component so as to reduce the risk of contamination.